Biostatus and Distribution

The Native shield-bug egg parasitoid is found in Australia and New Zealand. In New Zealand, this native species parasitises the eggs of native and Australian shield bugs in the family Pentatomidae (Hemiptera). It is found in native ecosystems as well as parks and gardens.

Conservation status: A native parasitoid of the eggs of native and Australian shield bugs in native habitats and gardens and parks.

Life Stages and Annual Cycle

In spring, adult female Native shield-bug egg parasitoids locate clusters of eggs of Shield bugs and Soldier bugs (Hemiptera: Pentatomidae). They lay an egg in each shield bug egg. The parasitised shield bug egg develops a black ring near the top. The wasp larva hatches and feeds on the developing bug, consuming all of it. When the wasp larva is full grown it pupates within the egg shell. When the adult is close to being fully developed, the upper half ot the shield bug egg darkens. When the adult wasp is fully developed, it sheds the pupal skin and when its body has hardened, it chews a hole in the top of the egg shell and emerges. There are several overlapping generations per year. They over-winter as mated females.

The adult wasps are black and have large heads and thorax (middle part of the body) and a relatively small abdomen. The dorsal (top) of the head and thorax are covered with punctures. The dark legs (3 pairs) and the antennae are tinged with small areas of reddish-brown. They have two pairs of wings that extend beyond the end of the abdomen.

The mated female can lay male and female eggs, but eggs laid by an unmated female only produce males.

Ron Cumber in his 1964 paper records his detailed observations on egg laying behaviour of the females of two Trissolcus species. When the Native shield-bug egg parasitoid is laying an egg, the wings of the female wasp are held vertically almost at right angles to the body and well away from the surface of the egg. After the wasp egg has been laid, the shield bug egg is marked by the tip of the ovipositor being wiped from side to side over the egg above the point of oviposition. This marking prevents the ovipositing wasp or another female wasp from laying an egg in the bug egg. However, it won’t prevent another species of egg parasitoid laying its egg in the shield bug egg.

Three images of the underside of adult Native shield-bug egg parasitoids, Trissolcus oenone (Hymenoptera: Platygasteridae): note the white setae (hairs on the underside of the abdomen of the adult on the right.

Recognition

Identification of the adult wasps requires expert knowledge. However, the name of the wasp parasitizing some shield bug (Pentatomidae) eggs can usually be determined by the colour of the eggs. The herbivorous shield bugs have relatively pale eggs, and when parasitised by the Green vegetable bug egg parasitoid the eggs turn black. When they are parasitised by the Native shield-bug egg parasitoid, the eggs have a black ring near the top of the egg and just before the wasp emerges, the top of the egg also turns black.

This method of parasitoid wasp identification will not work for the predatory Pentatomidae in New Zealand that lay black eggs. However, when the adult wasps have emerged, it may be possible to recognise the species.

Adult Native shield-bug egg parasitoids and Green vegetable bug egg parasitoids have stubby black bodies. The Native shield-bug egg parasitoid adults have dark legs and antennae with a few paler areas. The Adult Green vegetable bug egg parasitoids has pale reddish legs and the basal half of the antennae is also pale with the other half being black. The adults of the third species, Trissolcus maori Johnson, 1991, that parasitizes the eggs of the closely related family, Acanthosomatidae, are smaller than the other two species. Also it has light coloured legs and dark antennae.

Eggs of the Australasian green shield bug, Glaucias amyoti (Hemiptera: Pentatomidae) on the underside of a leaf of Coprosma robusta parasitized by the Native shield-bug egg parasitoid, Trissolcus oenone (Hymenoptera: Platygasteridae): note the black ring and dark top to the eggs, the latter indicating that the eggs are about to hatch.

Natural Enemies

No pathogens, parasitoids or predators of the Planthopper parasitoid, Dryinus koebelei are known in New Zealand. The adults are probably caught by predatory insects, spiders and birds.

Prey/Host

In New Zealand, the Native shield-bug egg parasitoid has been reared from native shield bugs (Pentatomidae), and three adventive species from Australia. Its hosts include both herbivores and predators (called Soldier bugs).

Eggs of the Australasian green shield bug, Glaucias amyoti (Hemiptera: Pentatomidae) on the underside of a leaf of Coprosma robusta parasitized by the Native shield-bug egg parasitoid, Trissolcus oenone (Hymenoptera: Platygasteridae): note the black ring and dark top to the eggs, the latter indicating that the eggs are about to hatch.